1. Field of the Invention
The present invention relates generally to a method and an apparatus for connecting a portable terminal to a Wireless Local Area Network (WLAN). More particularly, the present invention relates to a method and an apparatus for enhancing WLAN connection performance by turning on and off a Power Save Mechanism (PSM) function.
2. Description of the Related Art
Portable terminals are being researched and developed that have a Wireless Local Area Network (WLAN) function. More particularly, work is being done under the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard on techniques for reliable data transmission in the WLAN. For example, a method for guaranteeing reliability by using Request to Send/Confirm to Send (RTS/CTS) frames, as illustrated in FIG. 1, is suggested.
FIG. 1 illustrates a RTS/CTS scheme according to the related art.
Referring to FIG. 1, a source terminal (SRC) 111 having data 105 to transmit sends an RTS 101 to a destination terminal (DEST) 113. When the destination terminal 113 is capable of receiving data, the destination terminal 113 responds with a CTS 103. Another terminal (OTHER) 115 receiving the RTS/CTS is blocked from using the WLAN during times NAV(RTS) 121 and 123 required for the data transmission 105 by the source terminal 111, thereby guaranteeing reliable transmission.
Meanwhile, to reduce the power consumed by a WLAN module, the portable terminal adopts a Power Save Mechanism (PSM). An example of the PSM will be discussed below with reference to FIG. 2.
FIG. 2 illustrates a PSM according to the related art.
Referring to FIG. 2, when the portable terminal is compliant with the PSM, the portable terminal iteratively keeps the WLAN module in an awake state 203 based on a beacon interval 201 and switches the WLAN module to a sleep state 205. When there are packets to transmit and receive, the portable terminal stays in the awake state 203 by exchanging Traffic Indication Map (TIM)/ACKnowledgement (ACK) packets during the awake state 203 without transitioning into the sleep state 205. For example, when the portable terminal A 211 has a packet to send to the portable terminal B 213, the portable terminal A 211 transmits a TIM packet in the awake state 203. The portable terminal B 213, after receiving the TIM packet, sends an ACK to the portable terminal B 213 in the awake state 203 and then communicates data by exchanging packets without entering the sleep state 205. In contrast, the portable terminal C 215, which does not have any packets to transmit and receive, changes from the awake state 203 to the sleep state 205. Herein, each individual portable terminal using the PSM periodically stays in the awake state in order to receive multicast and broadcast packets, as described below with reference to FIG. 3.
FIG. 3 illustrates a relation between beacon and DTIM according to the related art.
Referring to FIG. 3, a beacon interval 301 and a Delivery Traffic Indication Map (DTIM) interval 303 are shown. The DTIM interval 303 is periodic. During the DTIM interval 303, each individual portable terminal using the PSM stays in the awake state in order to receive multicast and broadcast packets.
As for the multicast and broadcast frames, which are sent to an undefined number of the portable terminals, RTS/CTS may not be used and thus reliable transmission may not be achieved. Since the portable terminals using the PSM stay in the awake state to receive the multicast and broadcast packets only in the defined periodic interval, the portable terminals may not receive the multicast and broadcast frames. More specifically, in the WLAN connection procedure, the portable terminals may not receive the multicast and broadcast packets, such as Dynamic Host Configuration Protocol (DHCP) and Extensible Authentication Protocol (EAP). Accordingly, a probability of a failure of the WLAN connection is high. Portable terminals compliant with the IEEE 802.11 standard have the PSM function enabled and thus the multicast and broadcast packets may not be received. As a result, the probability of the WLAN connection failure rises.